1. Field of the Invention
The present invention relates to a semiconductor package. More specifically, the present invention discloses a ball grid array semiconductor package having a resin coated substrate with a metal core.
2. Description of the Prior Art
As electronic devices have become more compact and with more features, integrated circuits utilized in such electronic devices have been required to be reduced in size while transistor count inside the device has increased.
As a result, semiconductor packaging has continually advanced. Currently, a popular packaging method is the ball grid array (BGA). This type of semiconductor device uses balls for conductive leads in place of traditional wire leads.
Refer to FIG. 1, which is a sectional view showing the construction of a conventional BGA semiconductor package.
The conventional BGA device includes a semiconductor chip 102 having an integrated circuit and a plurality of signal input/output pads 104. The chip is bonded to the central portion of the upper surface of a printed circuit board (PCB) 110 by a bonding layer 106. The PCB 110 comprises a resin substrate 111 having a circuit pattern on each of the upper and lower surfaces. The circuit patterns on the upper and lower surfaces of the substrate 111 are formed by a plurality of conductive traces 112, 113, respectively. The conductive traces 112 and 113 are coated over with a high molecular resin solder mask 130.
A chip pad 116 is formed on the central portion of the upper surface of the resin substrate 111 to receive and mount the chip 102. The chip 102 is bonded to the pad 116 by a bonding layer 106. A plurality of first conductive traces 112 are formed on the upper surface of the substrate 111 at predetermined intervals, thereby forming an upper circuit pattern. The upper circuit pattern is coated with a solder mask 130. A plurality of second conductive traces 113 are formed on the lower surface of the substrate 111 and are each electrically connected to an associated one of the first conductive traces 112 through conductive via holes 114. A circular solder ball land 115, having a double-layered construction comprising a nickel layer 115b and a gold layer 115c, is formed on each of the second conductive traces 113 through an electrolytic plating process. A solder ball 120, is welded to each of the solder ball lands 115 and is used as a signal input/output terminal of the package 100 during signal communication of the package 100 with a main board (not shown). The signal input/output pads 104 of the chip 102 are electrically connected to the first conductive traces 112 using wires 140. The semiconductor chip 102 and the wires 140 are covered using an epoxy molding compound thereby forming an envelope 150 on one side of the package.
The conventional BGA device as described above, has several disadvantages. For example, the multiple masking processes and the number of processing steps and materials make such devices relatively expensive. In addition, the PCB substrate of the conventional device does not easily dissipate heat and is therefore susceptible to problems associated with temperature.
Therefore, there is need for an improved ball grid array semiconductor package with improved thermal performance, higher reliability, and lower cost.
To achieve these and other advantages and in order to overcome the disadvantages of the conventional method in accordance with the purpose of the invention as embodied and broadly described herein, the present invention provides a ball grid array semiconductor package having a resin coated substrate with a metal core with improved thermal performance, higher reliability, and lower cost.
The BGA semiconductor package with resin coated metal core in accordance to an embodiment of the present invention comprises a metal core, resin substrate covering, solder balls, chip adhesive material, a chip, bonding wires, and encapsulant.
The metal core is, for example, a metal lead frame that is utilized in a conventional lead frame semiconductor package. The metal core is made from a conductive material, for example, copper material. Electrically conductive paths may be formed in the metal frame to create paths for electrical signals to be routed as desired. The metal core is coated with a resin to form a metal core resin covered substrate structure.
The semiconductor chip is adhesively bonded to the resin coated substrate having a metal core by means of an adhesive.
A plurality of bonding wires are bonded or attached between conductive contacts or traces on the active side of the semiconductor chip and the metal core. It should be noted that the resin coating covers both sides of the metal core except for selected areas of the metal core. For example, where it is desired to attach the bonding wires or the solder balls.
The bonding wires are utilized to create selective electrical connections between conductive contacts, pads, or traces on the semiconductor chip and the metal core.
A plurality of solder balls are formed which are electrically connected to the metal core. The solder balls are formed from, for example, Pb, Sn, or other conductive material. The solder balls act as electrodes of the semiconductor device and allow flow of input and output signals between the semiconductor chip and printed circuit boards, frames, or devices on which the semiconductor device is electrically connected.
A liquid encapsulant is formed to cover desired areas of the resin coated substrate, bonding wires, adhesive material, and semiconductor chip. The encapsulant is formed by, for example, printing or molding methods. The encapsulant adhesively fixes and protectively seals the semiconductor chip to the resin coated substrate thereby shielding the semiconductor chip and the bonding wires from the external environment. Additionally, since the substrate is of resin material, the adhesion between the substrate and the encapsulant is much stronger than if a standard metal core substrate was used.
The present invention comprises covering the metal lead frame structure with a resin. The encapsulant of the semiconductor device of the present invention adheres to the resin material. Since the encapsulant and the resin may be of similar materials, the thermal expansion properties are similar and the adhesion between the substrate and the encapsulant is much greater.
Additionally, the heat dissipation properties of the metal core are better than a substrate made solely of resin. Therefore, the thermal performance of the semiconductor device of the present invention is superior.
Furthermore, in an embodiment of the present invention, since the substrate of the present invention comprises a conventional lead frame metal core coated with resin, the production cost of the semiconductor device is lowered. This is due to the fact that the substrate of the present invention utilizing the metal core as conductive paths is less expensive to produce than a resin substrate which requires additional manufacturing processes to provide electrically conductive paths. An advantage of the present invention is that by utilizing inexpensive metal lead frames for the metal core, production costs are lowered.
A common concern with semiconductor devices is the floor life, moisture level, and moisture resistance. Industry standards and requirements are available for moisture/reflow sensitivity for devices. In these specifications, certain standards are given such as moisture resistance, moisture classification level and floor life.
An advantage of the present invention is that by utilizing the resin coated metal core substrate, the semiconductor device of the present invention is capable of consistently meeting the highest level requirements. This not only greatly reduces inventory management and cost of said management, but also allows devices to operate longer without succumbing to failure due to moisture or high temperature.
Another advantage of the present invention, is that due to the electrical characteristics and properties of the resin coated metal core substrate, the semiconductor device exhibits improved operation in high frequency applications.
Therefore, the present invention provides a ball grid array semiconductor package having a resin coated substrate with a metal core with improved thermal performance, higher reliability, and lower cost.
These and other objectives of the present invention will become obvious to those of ordinary skill in the art after reading the following detailed description of preferred embodiments.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.